208 



at the base velocity station (station 37) is required. The coordinate 

 increments to the current due to the flow through the branch channel 

 extending from near Biddies Point to the Delaware are computed 

 from the head in this channel. As this correction is small, the tides 

 at the Delaware entrance to this branch may be taken as the same 

 as those at the entrance to the main canal, at station 5. From the 

 tabulated data, in this branch: 



i7 sin i?°= -2.29- (-2.45) = +0.16 



i? cos i7°=- 1.30- (-1.33) = +0.03 



tani?° = 5.33 H° = 79°20' 77=0.16 



The length of the branch channel is 9,000 feet. Taking the bottom 

 depth as 6 feet below datum, or 8.63 feet below mean tide, the bot- 

 tom width as 50 feet, and the side slopes as 1 on 2, the area of the 

 cross section is 580 square feet, the surface width is 85 feet and the 

 hydraulic radius, r, is 6.8 feet. The corresponding value of C is 82. 

 From this data: 



0=13°4O' 5=0.965 /3=-24°20' 



Whence 



m=2400/580=4.14 

 (B/m) sin /3=— 0.10 (B/m) cos j8=+0.21 



These increments evidently are to be subtracted, together with the 

 intervening storage, from the values of (B/m) sin jS and (B/m) cos j3 

 at station 19 + 500 to give the values at station 7 + 500. 



The values of (B/m) sin /S and {B/m) cos /3 at station 51+200, 

 enclosed in parentheses, are interpolated between those at the adja- 

 cent velocity stations. These values are disregarded in the summa- 

 tions by which the entries in columns (7) and (8) are derived. 



The recomputed amplitudes and phases of the currents at the 

 velocity stations are so close to those derived from the first computa- 

 tion that a recomputation of the heads is not made. 



401. Summary of results. — The amplitudes and phases of the com- 

 puted primary tides and currents, at the stations at which the actual 

 tides and currents were observed, are shown in the following tabu- 

 lation. 



Computed primary tides and currents, Chesapeake and Delaioare Canal 



